An engine of a motorcycle has a balancer device so as to reduce vibrations generated in association with reciprocal movement of a piston and rotation of a crankshaft (for example, refer to Patent Document 1). In an engine disclosed in Patent Document 1, a balancer shaft having a weight is configured to rotate in conformity to rotation of a crankshaft, so that periodic rotation vibrations of the crankshaft are cancelled.
Patent Document 1: Japanese Patent Application Publication No. H09-329196A
In the engine of Patent Document 1, when attaching the balancer shaft to a crank case, the weight is disposed at a predetermined position in advance and the balancer shaft is inserted into a shaft hole of the crank case and a shaft hole of the weight from an outside of the crank case. Like this, according to Patent Document 1, the balancer shaft and the weight are separately attached to the crank case, so that a mounting operation is troublesome.
In addition, when attaching the balancer shaft to the crank case it is necessary to phase-adjust the balancer shaft with respect to the crankshaft. In Patent Document 1, the crank case is formed with an opening for phase adjustment. The phase adjustment is performed by inserting a finger from the opening and rotating the balancer shaft.
Accordingly, in Patent Document 1, a mounting ability such as insertion of the balancer shaft to the weight and phase adjustment of the balancer shaft is poor. Also, a man-hour of forming the opening for phase adjustment at the crank case is troublesome.